Isolated Lingual Dystonia: A Rare Tardive Manifestation of Amisulpride

Abstract

Aims: To describe a rare case of isolated lingual tardive dyskinesia associated with prolonged low-dose amisulpride therapy and to emphasise the importance of early recognition and treatment. Presentation of Case: A 72-year-old woman with bipolar I disorder developed progressive dysarthria, dysphagia, and involuntary choreiform tongue movements after approximately 13 months of amisulpride therapy, initiated at 50 mg/day and titrated to 150 mg/day. Neurological examination showed continuous lingual movements with intermittent dystonic posturing, without limb involvement or other focal neurological abnormalities. Brain magnetic resonance imaging demonstrated only mild age-related cerebral atrophy, and routine laboratory investigations were within normal limits. Alternative structural, metabolic, seizure-related, and neurodegenerative causes were considered and excluded clinically. The Naranjo score was 6, and the WHO-UMC assessment classified the reaction as probable/likely. Amisulpride was discontinued, and tetrabenazine was initiated at 12.5 mg each morning and 25 mg each night. After six weeks, tongue movements and speech improved markedly, permitting dose reduction to 12.5 mg twice daily. Psychiatric stability was maintained with clozapine and sodium valproate/valproic acid. Discussion: The delayed onset, temporal relationship to prolonged dopamine receptor blockade, absence of an alternative cause, and improvement after withdrawal supported a tardive drug-induced movement disorder. Conclusion: Isolated lingual dystonia may occur during long-term low-dose amisulpride therapy. Regular movement assessment and prompt treatment modification may reduce functional impairment.